Method of making seals



April 24, 1945- R. L. BREADNER ET AL 2,374,269

METHOD OF MAKING SEALS Filed Oct. 30, 1943 2 Sheets-Sheet l CENTRIFUGE 1 /0 /0 ln'veni'ors:

' Robert L. Breadner,

John W Harvis, Charles H. Simms, b5 $14M Their At't'OTfi8H.

April 1945- -R. L. BREADNER ET AL 2,374,259

METHOD OF MAKING SEALS Filed Oct. 50, 1945 2 Sheets-Sheet 2 Fig 6. 1

CENTRlFUGE m.,s :dsm n S m r Ver... 0 O T a S IT .B .H mLW 4 T lfi W Wr v e ebm h m C T R Patented Apr. 24, 1945 METHOD OF MAKING SEALS Robert L. Breadner, Kenton, John W. Harris, North Wembley, and Charles H. Simms, Twickenham, England, assignors to General Electric Company, a corporation of New York Application October 30, 1943, Serial No. 508,434 In Great Britain September 23, 1942 7 Claims.

This invention relates to the manufacture of seals wherein electric conductors pass through a vitreous wall of the type wherein a plurality of metal Wires, rods or tubes (hereinafter called for brevity conductors) are arranged substantially along a circle round the axis of a vitreous tube and the wall through which they pass is continuous with the said tube. To this type belong stems adapted to be sealed into an aperture in a vitreous envelope; the said wall is then a flange extending outwards from the end of the said tube. To the same type belong. stems comprising ring seals; the said wall is then an annular piece joining the end of the said tube to the end of a second tube coaxial with it. Theinvention relates also to seals. of the type specifledand to electric lamps and discharge devices (which may be lamps) comprising such seals.

An object of the invention is to provide an improved method of making such seals which is suitable for mass production. Further objects and advantages of our invention will appear from the following description of species thereof and from the drawings in which Fig. 1 is an elevation, in section, of a die block with parts of the stem in assembled relation thereon; Fig. 2 is a similar view showing, in addition, a plunger for molding the seal; Fig. 3 is a similar view showing the apparatus during the molding operation; and Figs. 4 and 5 are views similar to Figs. 1 and 2 respectively, of a modified apparatus for making a stem of the type shown in sectional elevation in Fig. 6.

According to the invention in the manufacture of a seal of the type specified, the conductors are held in a block surrounding a vitreous tube and forming one part of a die; the end of the said tube protruding from the said block is heated and the system rotated so that the softened vitreous material is flung outwards by centrifugal force, so as to contact with the said conductors and preferably so as to flow around them; and finally a plungenforming the other part of the die, is pressed onto the surface of the said softened vitreous material in such a manner that a wall of the desired shape is formed through which the conductors are sealed.

If the sealto be manufactured is a stem of the first aforementioned (Figs. 1-3), nothing more than has just been stated is necessary. But preferably the vitreous tube is fed through the block while its end is being heated, so thatthe wall formed (which will be a flange round the tube) contains more vitreous material than that part of the tube which was first heated. Preferably also the said block is provided with a rim that limits the outward motion of the vitreous material. a

In.- Fig. 1, representing the first stage, I is the first said part of the die block, 2 the wires supe. ported in it, 3 the said glass tube, 4 the said rim of a cavity on the die block. Fig. 2 shows the second stage in which the end of the tube 3 has been heated (for example, by a burner '9), being pushed upwards during the process by a pusher rod l0, and the glass has been flung outward around the wires to form at least the embryo of a flange 5. Fig. 3' shows the next stage where the plunger part 6 of the die has been brought down, so that the upper ends of the wires enter recesses I (see Fig. 2) in the part 6, and the lower part of 6 has pressed the flange 5 into its final shape. In order that a bead should be formed around each wire, the parts I and 6 are recessed round each wire as shown at 8 (Figs. 1 and 2).

It will be observed that the length parallel to the axis of thetube in which the whole of the seal is contained is reduced to the minimum possible. Such short stems are known to be advantageo'us in many devices, e. g., fluorescent lamps, in which it is desirable that an electrode to which the conductors lead should be as near as possible to the envelope.

On the other hand, if a ring seal is to be manufactured, other things are necessary ordesirable. The block must lie in the space between the two said coaxial tubes, and the ends of these tubes must be approximately coplanar. Since the end of the outer tube may be (and indeed should be) softened at the same time as the end of the inher tube, it is preferably prevented from moving outwards'by a roller pressing against it as the system rotates. Preferably the plunger is associated with two members terminating in two cones, one a male cone entering the inner tube and the other a female cone into which the outer tube enters, which prevent the vitreous material from being squeezed beyond the continuations of the surfaces of the inner and outer tubes; the plunger then comes down in the space between the two said members. I

Referring to Figs. 4 and 5, 11 is the die-block in which the wires I2 to be-embedded are held. Only two wires are shown; there will usually be others outside the plane of the figures. I3 is the inner and H the outer glass tube. I

Fig. 4 shows the first stage in which the aforesaid parts are brought into their appropriate relative. position. In the lower half of Fig. 5 the open ends of the tubes have been united by s0f In the upper half of Fig. is shown the plunger which is now brought down on the lower-half.

It consists of a cylinder [8, hollow at its lower end, with recesses I! in its wall into which the upper ends of the wires l2 can pass. The flat end of the cylinder l8 presses the glass around the wires l2 between itself and the upper surface 20 of the block ll. Within the hollow space is a rod 2 I, tapered at its lower end, which end passes into the interior of the tube l3. Around the hollowed end is the annulus or sleeve 22, flared at its lower end, which end passes outside the tube 14. The. rod 2| and annulus 22 are connected by the pin 23 which slides in a slot in the cylinder l8; they are brought down into contact with the glass just before the plunger l8 presses on the glass.

When the plunger is lifted again and the stem separated from the die-block II, the stem has the form shown in Fig. 6. 24 is the wall connecting the tubes l3 and I4, through which wall the wires l2 pass.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The method of making seals of the class described which comprises assembling a vitreous tube and metal conductors at the exterior of said tube extending longitudinally thereof, applying heat to fuse the end of said tube while centrifuging the assembly to throw the softened glass outward around the conductors, and then pressing the softened glass around the conductors by pressure applied longitudinally of the tube.

2. The method of making seals of the class described which comprises inserting a glass tube into another hollow glass body with metal conductors extending longitudinally therebetween, and applying heat to fuse adjacent portionsof said tube and body while centrifuging the assemmetal conductors extending longitudinally of said tubes and therebetween, and applying heat to fuse the ends of the tubes whil centrifuging the assembly to throw the softened end of the inner tube outward against the said conductors and the adjacent end of the outer tube and while also restraining the fused end of the outer tube during. the centrifuging.

4. The method of making seals set forth in claim 3, including the further step of compressing the fused joint at the ends of the tubes by pressure applied longitudinally of the tubes.

5. The method of making stems of the type described which comprises assembling a glass tube and lead-in wires at the exterior of the tube extending longitudinally thereof and beyond an end thereof, applying heat to fuse the said end of the tube and centrifuging the assembly to throw the plastic glass outward around the lead-in wires while feeding the tube longitudinally in the direction of the heated end and supporting the outwardly thrown glass on a surface extendingtransversel of the tube to thereby form a lateral flange portion in which portions of the lead-in wires are embedded.

6. The method of making stems of the type described which comprises assembling a glass tube and lead-in wires at the exterior of the tube extending longitudinally thereof and beyond an end thereof, applying heat to fuse the said end of the tube and centrifuging the assembly to throw the plastic glass outward around the lead in wires while feeding the tube longitudinally in the direction of the heated end and supporting the outwardly thrown glass on a surface extending transversely of the tube to thereby form a lateral flange portion in which portions of the lead-in wires are embedded, and then compressing said lateral flange portion longitudinally of the tube to flatten it to final form.

7. The method of making stems of the type described whichcomprises assembling a single glass element in the form of a tube, and lead-in wires at the exterior of the tube extending longitudinally thereof and beyond an end thereof, 

